Repetitive Stimulation (Neuromuscular Junction)
Repetitive stimulation techniques can be used in diagnosing diseases of the neuromuscular junction; however, technical errors can give erroneous results, and careful attention to technique is essential.
For 24 hours before testing the patient must discontinue any medication that affects the neuromuscular junction.
The muscle and joint(s) it crosses are immobilized to minimize movement artifact, and the stimulating and recording electrodes are secured to avoid any movement. Immobilization is best achieved with muscles stretched and joint(s) extended.
The skin temperature is maintained at 34°C (94°F) to avoid false-negative results.
All stimuli must be supramaximal.
In myasthenic syndrome (Lambert-Eaten syndrome), the deficit is present in any muscles tested.
If the patient is suspected of having botulism, any clinically weak muscle is tested.
In myasthenia gravis, muscle weakness increases with exertion but improves with rest and with anticholinesterase drugs. Proximal muscle testing is much more sensitive than distal muscle testing; however, testing proximal muscles is technically more difficult.
Proximal Stimulation
Facial nerve: Stimulate behind the earlobe at the stylomastoid foramen with the active recording electrode over the nasalis muscle.
Brachial plexus/axillary nerve: Stimulate at Erb’s point with the active recording electrode over the deltoid muscle. This technique is painful, and movement artifact can be a problem.
Musculocutaneous nerve: Stimulate in the axilla with the active electrode over the biceps muscle. With this technique, the stimulus can be unstable.
Femoral nerve: Stimulate in the inguinal region with the active electrode over the vastus medialis muscle. This technique can be painful.
Spinal accessory nerve: Stimulate the nerve as it descends along the posterior border of the sternocleidomastoid muscle with the active electrode over the upper trapezius at the angle of the neck and shoulder. The patient is upright in a chair; the arms are adducted and extended with the hand holding the bottom of the chair. Exercise is obtained by having the patient shrug the shoulders against his/her own resistance.
Distal Stimulation
Ulnar nerve: Most investigators test the ulnar nerve distally. Stimulate the ulnar nerve at the wrist with the active electrode placed over the abductor digiti minimi muscle.
Median nerve: Stimulate the median nerve at the wrist with the active electrode over the abductor pollicis brevis muscle. The disadvantage of this technique is that the thumb is difficult to immobilize.
During each portion of the test (the single response, the 2 per second(s) stimulation, the 10-s postexercise), the potential amplitude often decreases during the first four responses. Thus, most investigators measure the fifth responseRelated posts:
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